Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-514580 (Abstract, Paragraphs [0038], [0040], FIG. 2) describes a driving control device that performs course tracking control. In cases in which an inter-vehicle distance between the vehicle and the leading vehicle is less than a limiting distance, and/or in cases in which an angle between a front-rear direction axis of the vehicle and a line of sight from the vehicle to a central point on a rear face of the leading vehicle (a tow angle) is less than a limiting angle, automatic control is performed such that the vehicle tracks the driving course of the leading vehicle.
When the inter-vehicle distance is the limiting distance or greater or the tow angle is the limiting angle or greater, the driving control device of Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-514580 disengages the course tracking control. Since situations in which the inter-vehicle distance becomes large and situations in which the tow angle becomes large, for example on curves, arise frequently, the limiting distance and the limiting angle need to be set higher in the driving control device of Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-514580 so that course tracking control does not disengage so readily. However, performing course tracking control in a situation where the inter-vehicle distance is great, or in a situation of driving along a curve, presents the following issue.
In cases in which the inter-vehicle distance is great, the distance between the onboard camera and the leading vehicle is great. Thus, the detection precision with respect to the leading vehicle based on images captured by the onboard camera is low compared to cases in which the inter-vehicle distance is small. Moreover, in cases in which the degree of curvature of a curve is great, specifically, cases in which the radius of curvature is small, it is difficult to image the rear face of the leading vehicle using the onboard camera. Thus, the detection precision with respect to the leading vehicle based on images captured by the onboard camera is low compared to when driving along a straight road. Thus, erroneous recognition by the vehicle that the leading vehicle is moving in a lateral direction sometimes occurs even when the leading vehicle is stably driving along the center of a vehicle lane. Erroneous recognition may produce errors in steering control, and destabilizes the driving of the vehicle. In cases in which the error is great, course tracking control itself can become difficult.